The invention relates to a regulatable pump, in particular a vane pump, in accordance with the type defined in greater detail in the preamble of claim 1.
DE 33 33 647 C2 discloses a regulatable pump having radially displaceable vanes and a cam ring whose eccentricity can be adjusted by means of a regulating piston, a journal of the cam ring lying between a counter support having a compression spring and a regulating piston. The position of the cam ring determines the size of the eccentricity and therefore the delivery rate of the pump. The regulating piston is clamped between the housing and the journal or stud of the cam ring for the purpose of adjusting the eccentricity. A linear load accordingly occurs between the journal and the regulating piston. It has turned out in practice that after sustained running, severe traces of wear are apparent both on the regulating piston and on the journal of the cam ring. Because of the highly dynamic loads acting on the cam ring, the latter is caused to vibrate, the vibration being transmitted to the journal of the cam ring or to the regulating piston exclusively via the linear contact. These vibrations are one of the main causes of the considerable wear phenomena. The wear can cause changes, namely an increase in the eccentricity, which in the most disadvantageous case leads to the rotating parts jamming and therefore to a failure of the pump.
As regards further prior art, reference is made to DE 43 02 610 A1 which reveals a lubricating pump, in which the intention is for the delivery rate to be additionally and independently restricted via detection of temperature and/or speed. For this purpose, a wedge-shaped actuating element is provided which bears in linear contact against the circumference of the cam ring and which, together with the regulating piston, influences or regulates the eccentricity of the cam ring.
The present invention is based on the object of providing a regulatable vane pump of the type mentioned at the beginning in which wear phenomena are, as far as possible, avoided.
According to the invention, this object is achieved by the features mentioned in claim 1.
By virtue of the fact that the journal of the cam ring is no longer wedged in linear contact between the regulating piston and the counter support, but that, in accordance with the invention, there is now surface bearing with simultaneous relief of load on the regulating piston, the disadvantageous traces of wear, as are the case in the prior art, no longer occur. The position of the cam ring is now determined by the surface bearing in the housing, as a result of which the piston can be mounted freely. This avoids the hitherto known distortions of the cam ring and of its journal and of the piston.